This invention relates to an intake manifold for an outboard motor and more particularly to an improved, lightweight and easily assembled intake manifold for such applications.
There has been an increasing emphasis toward the use of four cycle engines in outboard motors because of their more environmentally friendly nature. However, when replacing more conventionally employed two cycle engines, certain design challenges are presented. This is primarily due to the more complicated configuration of the engine, particularly when high specific outputs are sought.
The induction system for a four cycle engine is considerably different from that for a two cycle engine and hence, the induction system for four cycle outboard motors presents some unique problems. This is particularly true in conjunction with multi-cylinder engines and because of the fact that the engine is mounted so that the cylinder bores extend horizontally rather than vertically.
In connection with the induction system, it is generally the practice to employ a plenum chamber into which atmospheric air is drawn from within the protective cowling of the outboard motor. This plenum chamber then communicates with a plurality of throttle bodies and the cylinder head intake passages through manifolds, runners and intake manifolds. Thus, a fairly bulky and cumbersome arrangement result.
Also, it has been found that the length of the intake system between the plenum chambers and the cylinder head intake passages should be fairly large in order to provide the desired performance characteristics. This further complicates the design and mounting of the various components.
It is, therefore, a principle object of this invention to provide an improved, lightweight intake manifold for an internal combustion engine. It is a further object of this invention to provide an improved intake manifold for a four cycle outboard motor and particularly one having multiple cylinders.
It is a further object of this invention to provide an improved, simplified and easily assembled intake manifold for a four cycle outboard motor.
If the induction system is to be connected as a unit to the remainder of the engine, spatial problems may arise. This is particularly true if the assembly is done when the engine body is already mounted in the power head. Also these problems also exist when servicing completed outboard motors.
That is, it is important that the fit between the induction system and the remaining engine body be accurate. This is particularly true in matching the flow passages. Usually this alignment is accomplished by positioning studs in the engine body and particularly the cylinder head. These studs have non-threaded portions which serve the function of locating the intake manifold upon its attachment to the cylinder head. As will be described later by particular reference to FIG. 11, however, at times this is not possible, particularly when the engine body is already mounted in the protective cowling. This type of positioning arrangement requires a fairly substantial transverse clearance so that the induction system can be fitted not only over the threaded portion of the stud but also the non-threaded portion.
It is, therefore, a principal object of this invention to provide an improved manifold attaching system for the induction system of an outboard motor.
It is a further object of this invention to provide an improved and compact locating arrangement for such applications that minimize the spatial requirements required to assemble and disassemble the induction system from the engine body.